Crystal structure of bis{S-octyl-3-[(thiophen-2-yl)methylidene]dithiocarbazato-κ2 N 3,S}nickel(II)

The mononuclear nickel(II) complex is bis-chelated by dithiocarbazato ligands bearing a thienyl ring and an n-octyl alkyl chain.


Chemical context
Thiosemicarbazones, semicarbazones, hydrazide/hydrazones and dithiocarbazate ligands have been widely employed for the preparation of metal complexes. Over the last few decades, dithiocarbazate Schiff bases and their metal complexes have gained considerable interest because of their promising bioactivities against diverse cancer cell lines (Yusof et al., 2015;Ramilo-Gomes et al., 2021;Low et al., 2016), as well as antimicrobial activity . Clearly, the biological properties of these compounds can be modulated by using different organic substituents, leading to concomitant structural modifications (How et al., 2008;Yusof et al., 2022). A study of structure-activity relationships was described by Beshir et al. (2008).
Therefore, considering the diverse significance of dithiocarbazate bases and their role in a variety of biological applications, herein we report a novel Ni II complex with a dithiocarbazate Schiff base ligand bearing an octyl alkyl chain and a thienyl ring (Fig. 1).

Structural commentary
The nickel(II) atom is located on a crystallographic center of symmetry and exhibits a square-planar coordination sphere, being coordinated by two negatively charged N,S-chelating ligands in a trans configuration. The Ni-N1 and Ni-S1 bond distances are 1.9168 (19) and 2.1735 (7) Å , respectively with a chelating N1-Ni-S1 bond angle of 85.88 (6) . These values agree with those reported in previous papers (Begum et al., 2016;Islam et al., 2014;Howlader et al., 2015) for related compounds. It is worth mentioning that nickel(II) and copper(II) complexes with dithiocarbazate ligands have been reported to crystallize in both cis and trans configurations, although the latter is slightly more frequent (Begum et al., 2020).
All of the non-H atoms of the complex are almost coplanar, with S1 and C1 [À0.28 Å ] and C13, C14 [+0.24, +0.31 Å ], respectively deviating the most from its mean plane (r.m.s. deviation of fitted atoms = 0.135 Å ). The thienyl ring forms a small dihedral angle of 6.7 (1) with respect to the chelating five-membered ring. The long alkyl chain is in a staggered conformation with torsion angles along the chain that range between 176.7 (2) and 179.8 (2) .

Supramolecular features
The molecules stack with an interplanar distance of 3.623 (2) Å , and the crystal packing shows that all hydrophobic n-octyl chains segregate together, so as to share the same regions of space (Fig. 2), as already observed in similar complexes (Begum et al., 2016). Fig. 3 overlays this structure of the complex superimposed onto that of a 4-methoxybenzyl derivative (WEGKEB: Begum et al., 2018), where it is worth noting the different orientation of octyl chains in the two cases. This is due to the different torsion angle C6-S2-C7-     An ellipsoid plot (50% probability) of the title compound.
C8 of À177.36 (18) in this structure vs 86.8 (6) and À160.0 (9) (for the two disorder components of the equivalent torsion angle in WEGKEB), likely induced by crystalpacking requirements. Details of hydrogen-bonding interactions are given in Table 1.

Synthesis and crystallization
A solution of Ni(CH 3 COO) 2 Á4H 2 O (0.12 g, 0.5 mmol in 10 mL methanol) was added to a solution of S-octyl--N-(2-thienyl)methylenedithiocarbazate (0.314 g, 1.0 mmol in 30 mL of methanol). The resulting mixture was stirred at room temperature for 4 h. The dark-orange precipitate that formed was filtered off, washed with methanol and dried in vacuo over anhydrous CaCl 2 . Orange needle-shaped single crystals, suitable for X-ray diffraction, were obtained by slow evaporation of the compound from a mixture of chloroform and acetonitrile (4:1, v/v) after 14 days. Yield: 66%; m. p. (377-378) K.

Bis{S-octyl-3-[(thiophen-2-yl)methylidene]dithiocarbazato-κ 2 N 3 ,S}nickel(II)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.